Thanks for your contributions.
@Daniel : you're right, instead of voltage, I meant the resistance...
@Studiot : you're also right, the hemisphere correspond to an earth resistance located at the surface of the ground.
Having said that, suppose two points both buried in the ground and separated by a distance d. Is it posible to define the resistance between them if the medium in which they are buried is homogeneous and has got a resistivity Rho ?
Thanks and good evening
I went to the websites you kindly provided me with. Near the firsty one you quoted, I found an intersting site : http://gpg.geosci.xyz/en/latest/content/electromagnetics/principles_of_em_induction.html
If you go to this site, you canfind an interesting sketch :
where part of the signal sent to a transmitter to a receiver flows in the ground instead of using a nominal path at the surface of the ground.
This is exactly what I'm trying to do in dc ! I have several dc potentials (with respect to far earth) distributed at the top surface of the soil. Such potentials behave as current sources. For each of these dc currents sources, part of the current uses a nominal path to reach othe potentials on the surface, but another part uses the ground, including the far earth as a "secondary path". My goal is to modelise the soil between each of these ppoints as well as the far earth. Maybe I can try to draw something for you. Meanwhile, thanks again for your support.
Good night !